Conformal, Resilient Sulfide Membrane for 3D Silicon Anodes

The emergence of applications such as the Internet of Things (IOT) and the proliferation of increasing smaller medical devices require an equally small energy storage device. It is not clear that batteries can be simply decreased in size and still meet the energy and power requirements for these devices. Current planar electrodes try to meet this challenge by scaling the film thickness to achieve high areal capacities. However, this approach increases the diffusion lengths for both electrons and ions, which can severely degrade the rate performance. Three-dimensional (3D) electrodes are being explored as a means to maximize the areal capacity without limiting the power density. In order for this new electrode construction to reach its maximum performance, a high-conductivity, solid electrolyte must be employed. The conformal, resilient sulfide membrane described in this proposal meets all of these requirements. ADA’s low cost, high rate, and high-capacity microscale cell will be based on a 3D Si anode and a solution processable sulfide membrane. This process leverages the availability of low cost Si wafers from the integrated circuit and photovoltaic module industries. The solution processable sulfide membrane and blade cast cathode are both readily scalable to larger volumes and larger areas, and do not require high pressure densification steps that could potentially crack the Si wafer. The sulfide membrane will leverage the inherently high ionic conductivity of crystalline sulfides while a self-repairing polymer system with species capable of hydrogen bonding will provide elasticity. ADA will work with the National Renewable Energy Laboratory to demonstrate a sulfide membrane with an ideal combination of Li+ transport properties and mechanical cohesion and robustness throughout the drying process and cycling with the 3D Si anode. This uniform and conformal sulfide membrane layer will be critical for providing a physical barrier between the Si anode and NMC cathode throughout the volume changes of cycling, while also facilitating the ready and selective movement of Li+ during charging and discharging. ADA will synthesize the sulfide membrane and build cells, and NREL will provide the 3D patterned Si and carry out characterization. ADA’s partners Enersys and Boston Scientific will provide key guidance that will ensure the ultimate transition of the 3D Si/NMC cell into the marketplace. The successful integration of this conformal high-conductivity solid-state electrolyte will allow the further miniaturization of batteries, while maintaining high areal capacity and high-power density. This combination will allow applications including laptops, cell phones, video cameras, and hand-held power tools with substantially longer usage time between charges. The proposed battery technology will also enable medical applications such as drug delivery units, hearing aids and neurological stimulators. In defense applications, the proposed battery technology can enable specialized mobile power applications such as communication devices, unmanned air vehicles, and space vehicles.